The present invention relates to a wafer transfer and a wafer polishing apparatus, and more specially, to a wafer transfer and a polishing apparatus capable of sensing the existence of the wafer as well as the proper loading of the wafer.
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One process available for forming such interconnections is photolithography. A photolithographic process requires that surfaces on which pattern images are to be focused by a stepper should be as flat as possible because depth of focus of an optical system is relatively small. It is therefore necessary to make surfaces of semiconductor wafers flat for photolithography.
One customary way of planarizing the surface of the semiconductor wafer is to polish the semiconductor wafer by a CMP (Chemical Mechanical Polishing) process. The polishing apparatus to planarize the surfaces of the semiconductor wafers generally comprises a polishing table to which a polishing pad is attached, and top rings are employed to hold the semiconductor wafers onto the polishing table. In this polishing apparatus, semiconductor wafers are mounted on respective top rings, and then all the semiconductor wafers held by the top rings are simultaneously pressed down against the polishing pad on the polishing table, and then the wafers are polished.
An exemplary of polishing apparatus is disclosed in the U.S. Pat. No. 6,629,883 “Polishing apparatus” by Katsuoka, et al. According to the patent above-mentioned, the polishing apparatus has a transfer for transporting the semiconductor wafers from the top rings or to the top rings.
Referring to FIG. 10 in the U.S. Pat. No. 6,629,883 above-mentioned, wafer detecting sensors are provided at positioned spaced from the transfer. Each sensor is a photo-sensor comprising a light-emitting element and a light-receiving element. These sensors detect whether the semiconductor wafers are chucked on the transfer or not.
However, because the light-emitting and light-receiving elements are installed at a tilted position with respect to the surface of the semiconductor wafer, these sensors have a difficulty for sensing proper positioning of the wafer. Improper wafer positioning may lead to wafer damage in the subsequent processing or even breakdown of the semiconductor manufacturing apparatus, e.g. polishing apparatus.